Sculling oar

ABSTRACT

An object is to provide a Ro-scull which can suppress a decrease in thrust force by water resistance generated during turn-over operation and can realize high-speed cruise of a boat. The Ro-scull has a Ro-arm  1  and a Ro-blade  2  having a flat part  12  perpendicular to the Ro-arm  1 . The Ro-arm  1  is attached to an upper end portion of the Ro-blade  2  from an obliquely lower side. Namely, the Ro-arm  1  and the Ro-blade  2  are joined to each other while the Ro-arm  1  “receives” the Ro-blade  2 . A Ro-handle  3  is arranged not on the upper surface side but on the lower surface side of the Ro-arm  1.

TECHNICAL FIELD

The present invention is an invention related to a Ro-scull (or yuloh)(i.e., a sculling oar) which is operably attached to a ship in order tomanually propel the ship, particularly a small boat.

BACKGROUND ART

It is thought that the Ro-scull which is a traditional manually rowingapparatus was brought to Japan from China at around a time before theKamakura period. Since the Ro-scull was brought to Japan, the Ro-scullhad been gradually improved, and the final form of the Ro-scull wascompleted in the early Edo period. Then, the form of the Ro-scull hasbeen kept in substantially the same shape.

The Japanese Ro-scull has two features: (1) two rods of materials areused while being joined together; and (2) the two rods of materialsthereof are joined to form a bent configuration.

Particularly, the Ro-scull having the above features is called as“Tsuguro (joined Ro-scull).” On the other hand, the Ro-scull in whichtwo rods of materials are not used is called as “Saoro (rod Ro-scull).”

FIG. 6 shows a structure of the conventional Ro-scull.

The conventional Ro-scull consists of two large parts and two smallparts. Referring to the perspective view of FIG. 6, each structure willbe described.

In FIG. 6, the reference numeral 101 denotes a Roasi (hereinafter,Ro-blade or yuloh blade) which paddles the boat, and the Ro-blade 101has a spatula-shaped flat part 110. The reference numeral 102 denotes aRoude (hereinafter, Ro-arm or yuloh arm) which is rigidly fixed to theRo-blade 101 so as to be substantially horizontally held when the flatpart 110 is orientated to an obliquely upward direction. Near a jointportion between the Ro-blade 101 and the Ro-arm 102, there is no flatpart existing, but there is a part 120 (usually known as Ireko (insert))having a round shape. A user puts the part 120 on a shaft support part201 (usually called as Robeso (tholepin) or Rogui (Ro-stake or yulohstake) provided at a rear end portion of a boat 200, (or the part 120 isrotatably supported by the shaft support part 201). The operator of theboat operates the Ro-arm 102 from side to side, thereby moving theRo-blade 101 from side to side with the shaft support portion working asa pilot.

A small projected Rozuka (Ro-handle or yuloh handle) 103 is rigidlyfixed onto the upper surface of the Ro-arm 102 and the Ro-handle 103 isused with a rope called Hayao 104 being tied thereto. The other end ofthe Hayao 104 is rigidly fixed to the bottom side of the boat, and theHayao has a function of transmitting a thrust force to the boat when thethrust force is generated while the Ro-scull is operated.

The action of the conventional Ro-scull having the above structure willbe described below.

The operator operates the Ro-scull arm 102 from side to side so that theflat part of the Ro-blade 101 is inclined with respect to an advancingdirection. FIG. 7 shows the movement of a cross section of the Ro-blade101 in the time-series order at the position where the Ro-blade is incontact with a water surface when the operator operates the Ro-scull.Assuming that the advancing direction of the boat is the lower side ofthe drawing, a to c in FIG. 7 show the states each in which the Ro-blade101 is moved leftward with respect to the advancing direction of theboat, i.e. a to c in FIGS. 7 show a transition when the operator movesthe Ro-arm 102 rightward. In the cross section of the Ro-blade 101, thesign f denotes a front edge in the advancing direction of the Ro-blade101, and the sign r denotes a rear edge in the advancing direction ofthe Ro-blade 101.

A water flow generated in such a case relative to the Ro-scull is shownby a water flow 300 in (a) of FIG. 8.

As can be seen from the foregoing figure, a difference of flow in thewater flow is generated between the top surface and the bottom surfaceof the flat part 110 of the Ro-blade 101 by obliquely moving theRo-blade 101. The difference in the water flow creates a force similarto the force called “lift force” in an aircraft and the like, whereby, athrust force in a direction of an arrow 400 is generated. When,thereafter, the movement of the Ro-blade 101 is changed from theleftward to the rightward with respect to the advancing direction,namely, when the moving direction of the Ro-arm 102 is changed, theRo-blade is moved as shown in d to f of FIGS. 7.

In this case, a water flow 301 is created as shown in (c) of FIG. 8,and, as expected, the thrust force is generated in the direction of anarrow 401 similar to the direction of the arrow 400.

At a point in which the moving direction of the Ro-blade 101 is changedfrom the left to the right (the point between c and d of FIG. 7), it isnecessary that the inclination of the Ro-blade is reversed (usuallycalled as Kaeshi (turn-over)).

As can be seen from the above, among the manually rowing methods such asa paddle and an oar, the Ro-scull is the most functional in that thehydrodynamic lift force is used as the thrust force.

In an ideal condition, it is known that the lift force (thrust force)generated in the above-described manner is ten times as large as thedrag force generated. Namely, the lift is generated ten times the rowingforce.

Although the lift force is transmitted as a thrust force to a stern, theoperator does not sense the thrust force by an operator's arm becausethe Hayao 104 and the fulcrum of the Ro-scull receive the thrust force.Further, unlike other manually rowing apparatuses, the Ro-scull has nowasted motion because the thrust force is generated in both directionsof the reciprocating motion.

However, in the conventional Ro-scull, the flat part 110 obstructs thewater flow at the point of the turn-over. In this case, as shown in (b)of FIG. 8, the water flow orthogonally hits the flat part 110 of theRo-blade 101, so that resistance caused by the water flow is largelyincreased. In addition, large vortexes 302 are generated on thedownstream side of the water flow, which results in the decrease in thethrust force, and whereby, the thrust efficiency is remarkablydecreased.

In particular, because the vortexes are radically generated with theincreasing speed of the boat, the thrust efficiency worsens as the speedof the boat is increased, and actual high-speed cruise by the thrust bythe Ro-scull becomes difficult.

Therefore, in the case of the manually rowing boat with the Ro-scull,there is a problem that the speed of the boat becomes slower whencompared with the oar which generates the thrust force on the side ofthe boat.

DISCLOSURE OF THE INVENTION

In view of the foregoing, an object of the invention is to provide aRo-scull (i.e., a sculling oar), in which the operator is required touse only a small force by suppressing the resistance caused by thevortexes to the minimum during the turn-over, and thereby the high-speedcruise can be realized.

In order to solve the above problem, a Ro-scull according to theinvention is characterized by having a Ro-blade (i.e., second scull arm)which has a flat part (i.e., a flat scull blade), one end of theRo-blade to be located under a water surface; and a Ro-arm (i.e., afirst scull arm) which is attached to the other end of the Ro-blade at aposition where the Ro-blade is operated with reference to a positionwhere the flat part becomes perpendicular to the water surface.

Further, in a Ro-scull according to the invention, the Ro-blade isjoined to a connection part which is joined to a fin parallel to theflat part of the Ro-blade near a distal end portion of the other end ofthe Ro-blade which is not joined to the Ro-arm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view and a plan view of a Ro-scull according to anembodiment of the invention;

FIG. 2 is a perspective view of the Ro-scull according to the embodimentof the invention;

FIG. 3 is a transition view of a Ro-blade when the Ro-scull according tothe embodiment of the invention is operated from side to side;

FIG. 4 is a view showing a state in which the Ro-scull according to theembodiment of the invention is mounted on a boat;

FIG. 5 is an explanatory view explaining a relationship between theRo-blade of the Ro-scull according to the embodiment of the inventionand a water flow;

FIG. 6 is a perspective view of the conventional Ro-scull;

FIG. 7 is a transition view of the Ro-blade when the conventionalRo-scull is operated from side to side;

FIG. 8 is an explanatory view explaining the relationship between theRo-blade and the water flow in the conventional Ro-scull;

FIG. 9 is a view showing a Ro-scull to which a fin according to theinvention is attached;

FIG. 10 is a conceptual view of the Ro-scull and advancing speed;

FIG. 11 is an enlarged view of a distal end portion of the Ro-blade towhich the fin is attached;

FIG. 12 is a view showing the fin and a connection part;

FIG. 13 is a transition view of the Ro-blade when the Ro-scull, to whichthe fin is attached, is operated from side to side;

FIG. 14 is a conceptual view showing forces applied to the Ro-scull; and

FIG. 15 is a view showing adjustment of an incidence angle with respectto the distal end of a Ro-blade 2 when the fin is attached to theRo-scull.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Ro-arm-   2 Ro-blade-   3 Ro-handle-   4 Hayao (support line)-   5 fin-   6 connection part-   7 insert and fit portion

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a side view and a plan view of a Ro-scull according to anembodiment of the invention. Incidentally, the cross sections of theRo-scull at the corresponding points are shown above the side view.

As for the Ro-scull, the Ro-scull of the embodiment differs from theconventional Ro-scull in that the Ro-scull of the embodiment includes aRo-blade 2 (i.e., a second scull arm 2) having a flat part 12 (i.e., aflat scull blade 12) perpendicular to a Ro-arm 1 (i.e., a first scullarm 1). Because the Ro-scull of the embodiment may be formed when thefront edge f is located on the lower side and the rear edge r is locatedon the upper side, the attachment of the flat part 12 to the Ro-arm 1 isnot limited to a perpendicular direction. It is also possible that theflat part 12 is attached substantially perpendicular to the Ro-arm 1. Inthe conventional Ro-arm 102, the Ro-arm 102 is attached to the Ro-blade101 while the upper end portion of the Ro-blade 101 is covered with theRo-arm 102 so that the Ro-arm 102 is set in parallel with the watersurface. On the other hand, the Ro-arm 1 of the invention is attached tothe upper end portion of the Ro-blade 2 from the obliquely lower side.Namely, the Ro-arm 1 of the invention is characterized in that theRo-arm 1 and the Ro-blade 2 are fixed to each other while the Ro-arm 1“receives” the Ro-blade 2. As is apparent from FIG. 1, in the Ro-blade 2of the Ro-scull according to the invention, like the conventionalRo-blade 101, it is possible that a region where the Ro-blade 2 isjoined to the Ro-arm 1 may not be flat part 12. A Ro-handle 3 isarranged not on the upper surface side but on the lower surface side ofthe Ro-arm.

The flat part has a spatula shape as shown in the cross sectional viewof FIG. 1. As shown in the cross sectional view of FIG. 1, the flat part12 of the Ro-blade 2 has a shape in which the lower portion (front edgef) is thick and the upper portion (rear edge r) is thin. The lowerportion (front edge f) of the flat portion 12 becomes thinner toward thedistal end side of the Ro-blade 2. As the front edge f is thinned, thedistal end side becomes thinner as a whole, and the Ro-blade 2 has theso-called streamline shape in which the rear end portion r is alwaysthinner than the front end portion f (known as symmetrical wing shapewith no camber).

FIG. 2 is a perspective view of the Ro-scull according to theembodiment. As is apparent from FIG. 2, the surface of the conventionalRo-blade surface is formed with reference to a horizontal state. On theother hand, the Ro-scull of the invention differs from the conventionalRo-scull in that the surface of the Ro-blade of the invention is formedbased on the use in the perpendicular state and the Ro-arm 1 and theRo-blade 2 are fixed to each other while the Ro-arm 1 “receives” theRo-blade 2.

Further, the Ro-scull of the invention differs from the conventionalRo-scull in that the Ro-handle 3 to which the Hayao (support line) 4 isattached to the lower surface of the Ro-arm 1 (the upper surface of theRo-arm in the conventional Ro-scull) in order to set the perpendicularstate of the flat part of the Ro-blade 2 as the reference. Therefore,the perpendicular state is set as the reference.

FIG. 4 is a view showing a state in which the Ro-scull of the embodimentis mounted on the boat. As can be seen from FIG. 4, the conventionalRo-scull is at a standstill in a reversed V-shape, but on the contrary,it is clear that the Ro-scull of the embodiment is based on a V-shape.

In the embodiment, a part corresponding to the Ireko 120 of theconventional Ro-scull has a relatively high degree of freedom due to thestructure, so that the part corresponding to the Ireko 120 may be formedin the support shape of an usual oar.

The action of the Ro-scull formed in the above-described manner will bedescribed.

FIG. 3 shows the transition of the Ro-blade 2 when the Ro-scull of theembodiment is operated from side to side. FIG. 3 shows the movement ofthe cross section of the Ro-blade 2 (flat part 12) in the time-seriesorder at the position where the Ro-blade 2 is in contact with a watersurface, when the operator operates the Ro-scull.

In g to I of FIG. 3, like the conventional Ro-scull, the Ro-scull isoperated while it is inclined in an oblique direction. Namely, theRo-scull is operated from side to side while the front edge of the flatpart 12 of the Ro-scull is always inclined onto the advancing direction.Therefore, as shown in (a) of FIG. 5, a water flow 30 acts on the flatpart 12 in the same manner as for the conventional Ro-scull, so that thethrust force is generated in the direction of an arrow 40. For the waterflow to the flat part 12 of the Ro-blade 2 in the reversed direction, anincidence angle becomes reversed, and the thrust force is generated inthe opposite direction (direction of an arrow 41 in (c) of FIG. 5) tothe direction in which the Ro-blade 2 is moved as shown in g to h to i(or leftward).

The part of the turn-over is the feature of the embodiment.

Since the surface of the Ro-scull is perpendicular in a referenceattitude of the perpendicular Ro-scull, when turn-over operation of theRo-scull is performed at a repetitive point, the flat part 12 of theRo-arm 2 becomes parallel to the water flow. Therefore, as shown in (b)of FIG. 5, the resistance caused by the water flow becomes the minimum.The absence of the resistance means, as a matter of course, that thevortex is hardly generated on any one of the surfaces of the flat part12 of the Ro-blade 2. Accordingly, the decrease in thrust force causedby the turn-over is hardly generated, so that the high-speed cruise canbe realized.

In addition, because only the light force is necessary for the turn-overoperation, the operation in which the Ro-scull is operated from side toside can be performed faster when compared with the conventionalRo-scull. Therefore, the cruise performance is also improved.

The second feature of the embodiment is that, as described above, theRo-blade 2 and the Ro-arm 1 are configured so that the relationshipbetween the Ro-blade 2 and the Ro-arm 1 forms a V-shape when theRo-scull is at a standstill.

The V-shaped relationship between the Ro-blade 2 and the Ro-arm 1facilitates the appropriate turn-over of the Ro-blade 2 at a respectivepoint of the Ro-scull of the embodiment.

Namely, the first motion of the turn-over operation generates rotationmoment about an axis of the Ro-blade 2 in the water to naturallyintroduce the appropriate turn-over angle.

Further, the third feature is that the Ro-handle 3 is projected from thelower side of the Ro-arm 1. The Hayao 4 is tied at the distal end of theRo-handle so that the angle of the Ro-scull surface does not becomeexcessive.

Thus, the incidence angle can be controlled so as not to be excessivelyincreased, and the appropriate incidence angle can be substantially,automatically obtained according to the speed of the boat.

The term of incidence angle means the relative angle formed by a mainwater stream (the stream at the center of the water stream) and thecross section of the Ro-scull.

In the embodiment, the Ro-blade 2 and the Ro-arm 1 are obliquelyattached to each other, but as a result of examinations of the inventor,it is optimum that the attachment angle ranges about 7 degrees to 15degrees.

Then, a second embodiment according to the Ro-scull of the invention,the Ro-scull further with a fin 5 will be described. FIG. 9 shows theRo-scull of the second embodiment. (a) of FIG. 9 is a perspective view,(b) of FIG. 9 is a side view, and (c) of FIG. 9 is a plan view. FIG. 12shows the fin 5 and a connection part 6. The fin 5 is joined to theconnection part 6, and the connection part 6 includes an insert and fitportion 7 which can be inserted and fitted into the flat part 12 Theinsert and fit portion 7 is inserted and fitted into the flat part 12 sothat the fin 5 is positioned above the Ro-blade 2 (as shown in FIG. 9).

When the flat part 12 is viewed from a side (i.e. in the case of theside view of (b) of FIG. 9), because the Ro-blade 2 is put in the waterwhile the angle formed by the Ro-blade 2 and the water surface rangesfrom about 30 to 50 degrees, it is preferable that the angle α formed byan extension line of the fin 5 and the Ro-blade 2 (see FIG. 11) rangesfrom about 40 to 60 degrees (90 degrees−50 degrees≦angle α≦90 degrees−30degrees).

When the thrust force of the boat is obtained by using the Ro-scull, asa matter of course, the advancing speed of the boat is the same at anyportion of the boat. However, as shown in (a) of FIG. 10, the speed ofswing from side to side of the Ro-scull is proportional to a length lfrom a fulcrum O. Accordingly, the speeds are different from one anotherat each point of the distances l₁, l₂, l₃, and l₄ from the fulcrum O.When the advancing speed of the boat is set at v, as shown in (b) ofFIG. 10, it is found that the relative speed of the water flow and theincidence angle vary with the distance from the fulcrum O.

In the case of the Ro-scull as explained above, if twisting does notoccur in the Ro-scull, the water flow having the constant speed isgenerated in parallel with the advancing direction by the movement ofthe boat, but since the moving speed (in the direction perpendicular tothe advancing direction) becomes larger at the distal end of theRo-scull, both the relative speed of the water flow hitting the Ro-sculland the incidence angle are increased, which unnecessarily increases thedrag at the distal end portion of the Ro-blade 2. Namely, the waste isincreased.

Therefore, as shown in FIG. 9, the fin 5 is further attached to thedistal end of the Ro-blade 2 (flat part 12), which allows the Ro-blade 2to be automatically bent toward the direction in which the incidenceangle at the distal end is decreased.

FIG. 15 is a view showing adjustment of the incidence angle with respectto the distal end of the Ro-blade 2 (flat part 12), when the fin isattached to the Ro-scull. (a) of FIG. 15 shows how the Ro-scull ischanged from the fulcrum O of the boat at the position where theRo-scull is in contact with the water surface, and at the position nearthe distal end of the Ro-blade, by the cross section of the Ro-scull ateach position. A locus shown by a solid line indicates the locus of thecross section near the distal end of the Ro-blade 2, and a locus shownby a broken line is the locus of the cross section at the position wherethe Ro-scull is in contact with the water surface. When the operatoroperates from side to side the Ro-scull on the fulcrum O, the Ro-sculladvances toward the advancing direction (in FIG. 15, the Ro-sculladvances from the left side to the right side), which also allows thefulcrum O to advance toward the advancing direction (from the left sideto the right side).

In the case where the boat is located at the position of the fulcrum O₁,or in the case where the boat is located at the position of the fulcrumO₂ which is one stroke ahead of the fulcrum O₁, the cross section (x inthe fulcrum O₁ and X′ in the fulcrum O₂) near the distal end of theRo-blade 2 becomes parallel to the cross section at the position wherethe Ro-scull is in contact with the water surface, when the fin 5 is notattached to the Ro-blade 2. However, as described above, the positionnear the distal end of the Ro-blade 2 differs from the position wherethe Ro-scull is in contact with the water surface in the relative speed,so that the water vortexes are generated to increase the drag as shownin (b) of FIG. 15 (for the purpose of illustration, the connection part6 is deleted in (b) and (c) of FIG. 15).

However, when the fin 5 is attached to the portion near the distal endof the Ro-blade 2, due to the water resistance against the fin 5, thedistal end of the Ro-blade 2 is bent toward the direction in which theincidence angle is decreased. Therefore, the position near the distalend of the Ro-blade 2 is bent from x to y and from x′ to y′ (the anglesbetween x and y and between x′ and y′ range from about two degrees toseven degrees). Namely, the incidence angle at the distal end portion ofthe Ro-blade 2 is automatically decreased by utilizing bending momentapplied to the fin 5. As a result, the ideal incidence angle is obtainedalong the total length of the Ro-blade 2, and the drag caused by thewater flow is decreased as shown in (c) of FIG. 15.

Since the Ro-blade 2 is bent by the fin 5, it is preferable that theRo-blade is made of flexible material and yet having strength to acertain degree. Wood, FRP, carbon fiber, the light metal can be cited asexamples of the material for the Ro-blade 2.

For the Ro-scull shown in FIG. 9, the fin 5 is joined to the Ro-blade 2through the connection portion 6. However, it is also possible that thefin 5 is directly joined to the distal end portion of the Ro-blade 2without the connection portion 6 being provided.

Thus, when the fin 5 is provided in the Ro-blade 2, because it isexperimentally found that the fin 5 always acts in the direction inwhich the incidence angle is decreased irrespective of the rowingdirection of the Ro-scull, the drag at the distal end portion of theRo-blade 2 is decreased. Therefore, the force necessary for the rowingof the Ro-scull is decreased, and in addition the thrust force isincreased, which allows the boat to advance at a high speed whencompared with the case where the fin 5 is not attached to the scull.

The action of the Ro-scull will be described in detail while FIG. 13shows the movement of the cross section of the Ro-blade 2 (flat part 12)at the position where the Ro-blade 2 is in contact with the watersurface in the time-series order when the operator operates the Ro-scullin which the fin 5 is attached to the Ro-blade 2. The Ro-scull acts inthe same manner irrespective of the attachment of the fin 5 to theRo-blade 2.

In FIG. 13, the sign O denotes the fulcrum of the Ro-scull attached ontothe boat, and the broken line indicates an imaginary line of theRo-scull with respect to the Ro-blade 2 which is in contact with thewater surface. Accordingly, the operator can move the scull from side toside on the fulcrum O.

First, it is assumed that the Ro-blade 2 is positioned at m′ when therear portion of the boat (lower portion of the figure) in which theRo-scull is supported on the fulcrum O is located at m. At this point,because the operator does not move the Ro-scull, the Ro-blade 2 islocated perpendicular to (substantially perpendicular to) the boat.

Then, the operator of the Ro-scull moves the Ro-arm 1 so that the frontedge f of the flat part 12 of the Ro-blade 2 is faced toward theadvancing direction (it is assumed that the advancing direction of theboat is the lower side of the figure) (It is possible that the Ro-blade2 is moved in either the right direction or the left direction, but inFIG. 13, the operator moves the Ro-scull, such that the Ro-blade 2 ismoved on the fulcrum O from the right side to the left side with respectto the advancing direction of the boat, and such that the Ro-arm 1 ismoved on the fulcrum O from the left side to the right side with respectto the advancing direction of the boat).

FIG. 14 is a side view ((a) of FIG. 14) when the operator applies theforce to the Ro-scull, and a plan view ((b) of FIG. 14) when theoperator applies the force to the Ro-scull. In the operation describedabove, since the operator applies force F′ to the Ro-arm 1 on thefulcrum O, the Ro-blade 2 is rotated in the reverse direction by theforce F′ on the fulcrum O.

At this point, the Ro-arm 1 overcomes the water resistance received bythe Ro-blade 2, and the Ro-arm 1 starts the lateral movement. Becausethe Ro-arm 1 has the upper angle relative to the Ro-blade 2 (preferablyranging from 7 degrees to 15 degrees), the rotational movement isinduced about the longitudinal direction (on the extension line of theRo-blade 2) of the Ro-blade 2 in the water.

Then, the force with which the operator pushes laterally the Ro-arm 1acts on the upper side of the rotation axis in the longitudinaldirection, so that the distal end of the Ro-arm 1 is pressed forward.Namely, when viewed from the Ro-blade 2, the front edge f of theRo-blade 2 is automatically rotated in the desired rotation direction.In FIG. 13, when the operator applies the force F′ to the Ro-arm 1 onthe fulcrum O so that the Ro-blade 2 is moved from the left side to theright side with respect to the advancing direction of the boat, theRo-blade 2 is moved on the fulcrum O from the right side to the leftside (from the position m′ to the position n′) with respect to theadvancing direction of the boat, and the position of the boat alsoadvances from the position m to the position n by the thrust forceobtained by the Ro-scull.

The rotation of the Ro-blade 2 is continued until the front edge fbecomes parallel to the water flow in the advancing direction withrespect to the Ro-blade 2 which is freely moved, and the thrust force isgenerated until the front edge f becomes parallel. When the front edge fbecomes parallel, the thrust force is not generated, but, because thethrust force generated at an early stage of the rotation of the Ro-blade2 gives tension force to the Hayao 4, the rotation is stopped in themidway, and the Ro-blade 2 is stabilized in the water at the appropriateincidence angle.

The effect that stabilizes the incidence angle is generated by couplingthe Hayao 4 to the distal end of the Ro-handle 3 attached to the lowersurface of the Ro-arm 1.

Accordingly, the lateral force generated by the operator acts in thedirection in which the incidence angle of the Ro-blade 2 is decreased,and the tension force of the Hayao 4 acts in the direction in which theincidence angle is increased, so that the operator can easily operatethe Ro-scull.

In the position of the Ro-arm 1, since the moving range from side toside is restricted by the Hayao 4, when the Ro-blade 2 reaches theposition of n, the “turn-over” operation is performed so that the frontedge f of the Ro-blade 2 is faced toward the advancing direction side.In this case, the operator applies the force F which is opposite to theforce F′ to the Ro-arm 1 (the force on the fulcrum O from the right sideto the left side with respect to the advancing direction of the boat),which allows the boat and the position of the Ro-blade 2 to reach p andp′.

Because the operator moves the Ro-arm 1 with the force F from the rightside to the left side with respect to the advancing direction of theboat, the Ro-blade 2 is moved on the fulcrum O from the left side to theright side (from the position p′ to the position s′ through the positionq′) by the same action as described above.

Like the transition from the position n′ to the position p′, the“turn-over” operation is performed at the position s′ so that the frontedge f of the Ro-blade 2 is faced toward the advancing direction side,which applies the force F′ to the Ro-arm 1. Therefore, the boat and theposition of the Ro-blade 2 are moved from positions s and s′ to thepositions t and t′. Then, as with the transition from the position m′ tothe position n′, the operator applies the force F′ to the Ro-arm 1 fromthe left side to the right side with respect to the advancing directionof the boat, which allows the boat and the Ro-blade 2 to be moved fromthe positions t and t′ to the positions u and u′.

Thus, the operator moves the Ro-arm on the fulcrum O of the boat fromside to side, which allows the boat to obtain the thrust force toadvance toward the advancing direction.

When the fin 5 is attached to the Ro-scull, in the turn-over operation(the operation from the position n to the position p, and the operationfrom the position s to the position t), the distal end of the Ro-blade 2(flat part 12) is bent by the water resistance against the fin 5, sothat the ideal incidence angle is obtained along the total length of theRo-blade 2. Therefore, the resistance against the Ro-blade 2 isdecreased, and the thrust force is increased.

INDUSTRIAL APPLICABILITY

The invention is characterized by having the Ro-arm rigidly fixed to theother end of the Ro-blade at the position, where the flat part comes toa standstill so as to become perpendicular to the water surface, andtherefore, in the turn-over operation, the water resistance against theRo-blade is largely decreased when compared with the conventionalRo-scull, which allows the decrease in thrust force by the waterresistance to be prevented. Further, the force caused by the waterresistance is decreased during the turn-over operation, which allows theRo-scull to be operated at a high speed. Therefore, when compared withthe conventional Ro-scull, the Ro-scull of the invention can propel theboat at a high speed.

1. A sculling oar to generate a thrust force of a boat by an operationby an operator from side to side, the sculling oar comprising: a firstscull arm to be operated by an operator; and a second scull arm having aflat scull blade extending substantially perpendicular to a watersurface when the sculling oar is attached to the boat; wherein thesecond scull arm is joined to the first scull arm such that the firstscull arm is positioned substantially above a longitudinal axis of thesecond scull arm.
 2. The sculling oar according to claim 1, wherein thefirst scull arm and the second scull arm are joined at a position toform a V-shape with respect to the water surface.
 3. The sculling oaraccording to claim 1, wherein the first scull arm and the second scullarm are joined such that the first scull arm forms an angle of sevendegrees to ten degrees with respect to the second scull arm.
 4. Thesculling oar according to claim 1, wherein a front edge of the flatscull blade is thicker than a rear edge of the flat scull blade, and thefront edge is always positioned on an advancing direction side withrespect to the rear edge when the operator operates the first scull arm.5. The sculling oar according to claim 1, wherein an area near a partwhere the first scull arm and the second scull arm are joined has around shape.
 6. The sculling oar according to claim 1, wherein one endof the first scull arm is joined to a scull handle for attaching theretoa rope fixed to the boat.
 7. The sculling oar according to claim 1,wherein a connection part is joined to a distal end portion of the flatscull blade, and the connection part is joined to a fin parallel todistal end portion of the flat scull blade.
 8. The sculling oaraccording to claim 7, wherein the fin is positioned above the flat scullblade.
 9. The sculling oar according to claim 8, wherein an angle αformed by an extension line of the fin and an extension line of the flatscull blade ranges from about 40 degrees to about 60 degrees.
 10. Thesculling oar according to claim 7, wherein an angle α formed by anextension line of the fin and an extension line of the flat scull bladeranges from about 40 degrees to about 60 degrees.
 11. The sculling oaraccording to claim 1, wherein the material of the second scull arm isany one of wood, FRP, carbon fiber, and light metal.